Wireless, radio frequency (RF) smoke and fire detection and alarm systems are well known. In such systems, each of a plurality of smoke and fire detector and alarm units (hereinafter “detectors”) is capable of alerting a building occupant of a dangerous (i.e., smoke or fire) condition even if the occupant is not in proximity to the detector detecting the dangerous condition. These systems work by relaying wireless, RF, alarm signals between the detectors so as to cause the alarms in all of the detectors to sound and thereby alert occupants of the existence of the dangerous condition, even if it is in a remote area from the occupant's location.
For example, a house may have one detector in each of the basement, first and second floors. Should a fire occur in the basement, the basement detector detecting that condition both sounds an internal alarm and transmits an RF alarm signal. Another detector, say the first floor detector, sounds its own internal alarm when it receives the RF alarm signal from the basement detector, and also retransmits the RF alarm signal. The second floor detector sounds its internal alarm upon receiving the RF alarm signal (from either the basement or first floor detector) and also re-transmits the RF alarm signal.
Prior art detectors continue sounding their internal alarms even if the condition causing the alarm has abated until manually turned off. This can be annoying to the occupants and may defeat the purpose for which the system was installed if the occupants ignore the alarm. It also wastes energy, and in the case of battery powered detectors, results in shortened battery life.
One reason that the detectors may continue to sound their internal alarms, even after the dangerous condition has abated, is due to lingering transmissions of the RF alarm signal. For example, in the scenario described above, the basement detector sent a RF alarm signal which was received by either (or both) of the first and second floor detectors. One or both of the first and second floor detectors then re-transmitted RF alarm signals. However, even after the fire in the basement abated, the first and/or second floor detectors may still be in an alarm state, and hence may re-transmit a RF alarm signal. This may occur indefinitely, causing all of the detectors to sound their internal alarms even though the fire has been abated. Only manual shutdown can alleviate the problem.